- rebrand to "MarkPro" with modern UI design

- add real-time preview with syntax highlighting via Prism.js
- implement dark mode theme toggle
- add markdown toolbar with formatting buttons and keyboard shortcuts
- create settings panel with configurable options (autosave, real-time preview)
- add markdown cheatsheet panel with syntax reference
- implement toast notifications system
- add word/character counter
- improve responsive design for mobile devices
- store user preferences and content in localStorage

Author: TobiasMue91